Washboard model of gas–surface scattering

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Abstract
The conventional ‘‘hard cube’’ and ‘‘soft cube’’ models of gas–surface scattering are extended to incorporate the effects of surface corrugation. The proposed ‘‘washboard’’ model invokes the hard cube assumption of conservation of tangential momentum, but with respect to the local surface tangent at the point of impact of the molecule with the corrugated surface. Expressions are derived in the form of convenient single variable quadratures for the angular scattering distribution, the mean velocity and kinetic energy as a function of scattering angle, and the trapping probability. The model is applied to the scattering of argon atoms from smooth and corrugated faces of platinum. Results are compared to those from multidimensional stochastic trajectory simulations employing a realistic interaction potential and moving surface atoms. The washboard model is shown to have a far wider range of validity than the cube models, and to describe properly the transition from singly peaked near-specular scattering from smooth surfaces to doubly peaked ‘‘rainbow’’ scattering from highly corrugated surfaces.